Plomin Bred Animals with High Learning Ability to Other Animals

Plomin bred animals with high learning ability to other animals with high learning ability and animals with low learning ability to other animals with low learning ability. Those from high learning ability lines continued to show high learning ability while those from low learning lines continued to show low learning ability. In Plomin's work, learning ability

A) varied by the age of the animal.
B) was a totally learned behavior.
C) varied by the sex of the animal.
D) was influenced by genetics.